1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device and method of fabricating the same that can improve the production yield and aperture ratio.
2. Discussion of the Related Art
As a demand for various types of display devices increases with recent development of the information society, researches are actively continuing on flat panel display devices such as LCD (Liquid Crystal Display) devices, PDP (Plasma Display Panel) devices, ELD (Electro Luminescent Display) devices, FED (Field Emission Display) devices, VFD (Vacuum Fluorescent Display) devices and the like. Of such flat panel display devices, the LCD devices are drawing much attention due to their lightweight, thin profile, low power consumption, high picture quality, mass production advantages and simple driving method.
An LCD device displays images by individually supplying data signals to pixels arranged in a matrix form in accordance with video signals and controlling the light transmittance of each pixel. The LCD device is commonly driven by an active matrix (AM) method. The AM method is a method in which a switching device such as a thin film transistor (TFT) is added to each pixel and liquid crystal in each pixel is driven by a voltage applied thereto through the switching device.
The LCD device may be categorized into various display modes according to the type of liquid crystal. Of the various modes, the TN (twisted nematic) mode is commonly being used. The TN-mode LCD device turns ON/OFF an electric field perpendicular to the substrates and thus drives liquid crystal in such a manner that a director of the molecules of the liquid crystal can be at an angle of 0° to 90° with respect to the substrates. The TN-mode LCD device has such advantages as easy black and white display function, speedy response and low driving voltage. However, because the liquid crystal is driven perpendicular to the substrates, the TN-mode LCD device has a narrow viewing angle that causes viewing angle dependency. The viewing angle dependency means that the color or brightness of an image changes depending on the direction or angle at which a viewer views the LCD device.
In order to overcome such a disadvantage, researches are actively continuing on a new mode such as an in plane switching (hereinafter, referred to as IPS) mode LCD device in which liquid crystal is driven parallel to the substrates. When a voltage is applied, the IPS LCD device forms an in-plane electric field on a substrate and aligns the liquid crystal horizontally, thereby securing a wider viewing angle.
FIG. 1 is a plan view illustrating a unit pixel of an IPS-mode LCD device according to the related art. Referring to FIG. 1, a gate line 3 and a data line 1 formed of metal are arranged vertically and horizontally to define a unit pixel on a thin film transistor substrate of the LCD device. Although the LCD device generally includes a plurality of pixels defined by a plurality of gate and data lines, only one pixel is depicted in FIG. 1 for simplicity.
A switching device (e.g., thin film transistor (T)) including a gate electrode 4, a semiconductor layer (A) and source/drain electrodes 5 and 11 is formed near the crossing of the gate line 3 and the data line 1. The gate electrode 4 and the source/drain electrodes 5 and 11 are connected to the gate line 3 and the data line, respectively, thereby turning ON the switching device by a signal inputted through the gate line 3 and transmitting a data signal applied through the data line 1 to the pixel.
The IPS-mode LCD device further includes a common line 17 arranged parallel to the gate line 3 in the unit pixel for transmitting a common signal and at least one pair of electrodes, i.e., a common electrode 13 and a pixel electrode 15, for generating an in-plane electric field parallel to the substrate. The common electrode 13 is formed simultaneously with the gate line 3 and connected to the common line 17, and the pixel electrode 15 is formed simultaneously with the source/drain electrodes 5 and 11 and connected to the drain electrode 5 of the thin film transistor (T). A pixel electrode line 11 electrically connecting the pixel electrodes 15 overlaps the common line 17, with a gate insulation film (not shown) therebetween, and a storage capacitor (Cst) is formed in the unit pixel.
Because each pixel includes only one switching device, the IPS-mode LCD device has a problem in that the unit pixel may not properly work when the switching device is defective. Such a problem may occur not only in the IPS-mode LCD device but also in other mode LCD devices such as the TN-mode LCD device. In particular, the thin film transistors in the LCD device are formed through several deposition and etching processes in which several defects may occur. One of the most fatal defects is a short circuit between the gate electrode and the source or drain electrode, which creates a point defect in the LCD device.